1. Field of the Invention
Embodiments of the invention generally relate to methods and apparatus for creating an annular barrier in a well bore. More particularly, the invention relates to methods and apparatus for isolating at least a portion of a well bore from at least another portion of the well bore.
2. Description of the Related Art
As part of the well bore construction process, a hole or well bore is typically drilled into the earth and then lined with a casing or liner. Sections of casing or liner are threaded together or otherwise connected as they are run into the well bore to form what is referred to as a “string.” Such casing typically comprises a steel tubular good or “pipe” having an outer diameter that is smaller than the inner diameter of the well bore. Because of the differences in those diameters, an annular area occurs between the inner diameter of the well bore and the outer diameter of the casing and absent anything else, well bore fluids and earth formation fluids are free to migrate lengthwise along the well bore in that annular area.
Wells are typically constructed in stages. Initially a hole is drilled in the earth to a depth at which earth cave-in or well bore fluid control become potential issues. At that point drilling is stopped and casing is placed in the well bore. While the casing may structurally prevent cave-in, it will not prevent fluid migration along a length of the well in the annulus between the casing and the well bore. For that reason the casing is typically cemented in place. To accomplish that, a cement slurry is pumped down through the casing and out the bottom of the casing string. Drilling fluid, water, or other suitable fluid is then used to displace the cement slurry into the annulus. Typically, drillable wiper plugs are used to separate the cement from the well fluid in advance of the cement volume and behind it. The cement is left to cure in the annulus thereby forming a barrier to fluid migration within the annulus. After the cement has cured, the cured cement remaining in the interior of the casing string is drilled out and the cement seal or barrier between the casing and the formation is pressure tested. A drill bit is then run through the cemented casing and drilling is commenced from the bottom of that casing. A new length of hole is then drilled, cased and cemented. Depending on the total length of well several stages may be drilled and cased as described.
As previously mentioned, the cement barrier is tested between each construction stage to ensure that a fluid tight annular seal has been achieved. Typically the barrier test is performed by applying pressure to the casing internally. That is achieved by pumping fluid into the casing string from the surface. The pressure exits the bottom of the casing and bears on the annular cement barrier. The pressure is then monitored at the surface for leakage. Such testing is often referred to as a “shoe test” where the word “shoe” indicates the lowermost portion or bottom of a given casing string. When another well section is needed below a previously cased section, it is important that a successful shoe test be completed before progressing with the drilling operation.
Unfortunately cementing operations require cessation of drilling operations for considerable periods of time. It takes time to mix and pump the cement. It takes more time to allow the cement to cure once it is in place. During the cementing operations drilling rig costs and other fixed costs still accrue yet no drilling progress is made. Well construction is typically measured in feet per day and because fixed costs such as the drilling rig are charged on a per day basis that translates to dollars per foot. Because cementing takes time with zero feet drilled during the cementing operations those operations merely increases the dollar per foot metric. It is beneficial to minimize or eliminate such steps in order to decrease the average dollar per foot calculation associated with well construction costs.
Expandable well bore pipe has been used for a variety of well construction purposes. Such expandable pipe is typically expanded mechanically by means of some type of swage or roller device. An example of expandable casing is shown in U.S. Pat. No. 5,348,095 and that patent is incorporated by reference herein in its entirety. Such expandable casing has been described in some embodiments as providing an annular fluid barrier when incorporated as part of a casing string.
Expandable pipe has also been shown having non-circular (“folded”) pre-expanded cross-sections. Such initially non-circular pipe is shown to assume a substantially circular cross-section upon expansion. Such pipe having substantially the same cross-sectional perimeter before and after expansion has been shown (i.e. where the expansion comprises a mere “unfolding” of the cross-section). Other such pipe has been shown wherein the cross-section is “unfolded” and its perimeter increased during the expansion process. Such non-circular pipes can be expanded mechanically or by application of internal pressure or by a combination of the two. An example of “folded” expandable pipe is shown in U.S. Pat. No. 5,083,608 and that patent is incorporated by reference herein in its entirety.
As mentioned above, mechanical pipe expansion mechanisms include swage devices and roller devices. An example of a swage type expander device is shown in U.S. Pat. No. 5,348,095 and that patent is incorporated by reference herein in its entirety. An example of a roller type expander device is shown in U.S. Pat. No. 6,457,532 and that patent is incorporated by reference herein in its entirety. U.S. Pat. No. 6,457,532 also shows a roller type expander having compliant characteristics that allow it to “form fit” an expandable pipe to an irregular surrounding surface such as that formed by a well bore. Such form fitting ensures better sealing characteristics between the outer surface of the pipe and the surrounding surface.
Expandable pipe has been shown and described having various exterior coatings or elements thereon to augment any annular fluid barrier created by the pipe. Elastomeric elements have been described for performing such function. Coated expandable pipe is shown in U.S. Pat. No. 6,789,622 and that patent is incorporated by reference herein in its entirety.
Regardless of whether or not the cross-section is initially circular or is folded, expandable pipe has limitations of expandability based on the expansion mechanism chosen. When expandable pipe is deployed for the purpose of creating an annular fluid barrier the initial configuration of the pipe and the expansion mechanism used must be carefully tailored to a given application to ensure that the expansion is sufficient to create a barrier. If the chosen expansion mechanism is miscalculated in a given circumstance the result can be extremely disadvantageous. In that situation the expanded pipe is not useful as a barrier and further, because the pipe has been expanded retrieval may be impractical. Remedying such a situation consumes valuable rig time and accrues other costs associated with remediation equipment and replacement of the failed expandable pipe.
Therefore, a need exists for improved methods and apparatus for creating an annular barrier proximate a casing shoe that eliminates the necessity for cementing. There further exists a need for improved methods and apparatus for creating an annular fluid barrier using expandable pipe that provides for a successful recovery from a failed expansion attempt.